596 research outputs found
New Physics with three-photon events at LEP
The effect of the most general \z3gt vertex in the reaction e^+e^- \ra
3\gamma is studied with a particular attention to LEP searches. We give exact
analytical expressions including realistic cuts for the signal and present a
detailed analysis based on a Monte Carlo that includes the effect of the
irreducible QED cross section. As special applications we discuss the
effect of heavy scalars, fermions and gauge bosons and comment on the
``monopole" connection.Comment: No changes made from previous version, 34 pages, LateX, uses epsf, 11
.eps figs., full paper (including figs) is also available via WWW at
http://lapphp0.in2p3.fr/preplapp/psth/lastee3g.ps.gz or via anonymous ftp at
ftp:///lapphp0.in2p3.fr/pub/preprints-theorie/ftpee3g.u
Contribution of Scalar Loops to the Three-Photon Decay of the Z
I corrected 3 mistakes from the first version: that were an omitted Feynman
integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in
eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed
drastically. Doing an expansion in the Higgs mass I show that the matrix
element is identically 0 in the order (MZ/MH)^2, which is due to gauge
invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is
that the scalar contribution to this decay rate is several orders of magnitude
smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail,
OCIP/C-93-5, UQAM-PHE-93/0
Prevalence Rates of Mental Disorders in Chilean Prisons
PMCID: PMC371883
Characterization of heavily carbon-doped GaAs grown by metalorganic chemical vapor deposition and metalorganic molecular beam epitaxy
Carbon-doped GaAs with carbon concentrations ranging from 2~ 1Ol7 cmW3 to 2.6~ 102' cm -' has been characterized by variable temperature Hall effect measurements, secondary ion mass spectrometry (SIMS)) and double-crystal x-ray diffraction (DCXD). The samples studied were grown by metalorganic chemical vapor deposition (MOCVD) and by metalorganic molecular beam epitaxy (MOMBE). The hole mobility is dominated by degenerate conduction for hole concentrations > 1 X 1019 cma3, and the 77 K resistivity is typically 30%-35% lower than at 300 K in these samples. The mobilities of C-dopedp+-GaAs are found to be significantly higher than for Zn-or Be-doped p+-GaAs for doping concentrations in excess of 2x lo'* cmW3. The maximum achievable hole mobilities for C-doped material grown by the two techniques are nearly identical, indicating that neither MOCVD nor MOMBE has an inherent advantage over the other for producing low-resistivity p-type GaAs. SIMS analysis and Hall effect measurements reveal that the total carbon concentration, [Cl, is higher than the as-grown hole concentration, p, in the most heavily doped samples. DCXD measurements show general agreement with the lattice mismatch predicted by Vegard's law. However, for [C] > 102' cmm3 a discrepancy between the predicted and measured mismatch suggests that partial lattice relaxation or the presence of interstitial carbon may need to be considered in order to adequately describe the lattice contraction
Interacting mindreaders
Could interacting mindreaders be in a position to know things which they would be unable to know if they were manifestly passive observers? This paper argues that they could. Mindreading is sometimes reciprocal: the mindreader's target reciprocates by taking the mindreader as a target for mindreading. The paper explains how such reciprocity can significantly narrow the range of possible interpretations of behaviour where mindreaders are, or appear to be, in a position to interact. A consequence is that revisions and extensions are needed to standard theories of the evidential basis of mindreading. The view also has consequences for understanding how abilities to interact combined with comparatively simple forms of mindreading may explain the emergence, in evolution or development, of sophisticated forms of social cognition
Chargino-Sneutrino Production in Electron-Photon Collisions
We study the production of charginos and sneutrinos in electron-photon
collisions within the minimal supersymmetric standard model (MSSM). The high
energy photons can be generated by Compton backscattering of intense laser
pulses off one of the beams of the Next Linear Collider (NLC). This process
could offer a significant opportunity to identify sneutrinos, which exclusively
decay invisibly into a neutrino and the LSP, since the cross sections are two
orders of magnitude higher than for the radiative production of invisible
sneutrinos. For three scenarios of gaugino-higgsino mixing the cross sections
and polarization asymmetries are computed and the resulting signatures are
compared with the SM background.Comment: 22 pages, REVTEX, including 11 Postscript figures, complete psfile
also available at
ftp://ftp.physik.uni-wuerzburg.de/pub/preprint/1996/WUE-ITP-96-005.ps.gz ;
revised version: number of figures reduced, minor changes in text, final
versio
Is It Rational to Assume that Infants Imitate Rationally? A Theoretical Analysis and Critique
It has been suggested that preverbal infants evaluate the efficiency of others' actions (by applying a principle of rational action) and that they imitate others' actions rationally. The present contribution presents a conceptual analysis of the claim that preverbal infants imitate rationally. It shows that this ability rests on at least three assumptions: that infants are able to perceive others' action capabilities, that infants reason about and conceptually represent their own bodies, and that infants are able to think counterfactually. It is argued that none of these three abilities is in place during infancy. Furthermore, it is shown that the idea of a principle of rational action suffers from two fallacies. As a consequence, is it suggested that it is not rational to assume that infants imitate rationally. Copyright (C) 2012 S. Karger AG, Base
Supersymmetry Relations Between Contributions To One-Loop Gauge Boson Amplitudes
We apply ideas motivated by string theory to improve the calculational
efficiency of one-loop weak interaction processes with massive external gauge
bosons. In certain cases ``supersymmetry'' relations between diagrams with a
fermion loop and with a gauge boson loop hold. This is explicitly illustrated
for a particular one-loop standard model process with four-external gauge
bosons. The supersymmetry relations can be used to provide further significant
improvements in calculational efficiency.Comment: 21 pages of plain TeX + 5 PostScript figures (compressed and
uuencoded), UCLA/93/TEP/36 and DTP/93/8
The Search for Higgs particles at high-energy colliders: Past, Present and Future
I briefly review the Higgs sector in the Standard Model and its minimal
Supersymmetric extension, the MSSM. After summarizing the properties of the
Higgs bosons and the present experimental constraints, I will discuss the
prospects for discovering these particle at the upgraded Tevatron, the LHC and
a high-energy linear collider. The possibility of studying the
properties of the Higgs particles will be then summarized.Comment: 28 pages, latex, 15 figures, talk at WHEPP VII, Allahabad, Indi
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